import sys
#input = sys.stdin.readline
#input = sys.stdin.buffer.readline #文字列はダメ
#sys.setrecursionlimit(1000000)
#import bisect
#import itertools
#import random
#from heapq import heapify, heappop, heappush
#from collections import defaultdict 
#from collections import deque
#import copy
#import math
#from functools import lru_cache
#@lru_cache(maxsize=None)
#MOD = pow(10,9) + 7
#MOD = 998244353
#dx = [1,0,-1,0]
#dy = [0,1,0,-1]
#dx8 = [1,1,0,-1,-1,-1,0,1]
#dy8 = [0,1,1,1,0,-1,-1,-1]

class RollingHash():
    def __init__(self, s, base, mod):
        self.mod = mod
        self.pw = pw = [1]*(len(s)+1)
 
        l = len(s)
        self.h = h = [0]*(l+1)
 
        v = 0
        for i in range(l):
            h[i+1] = v = (v * base + ord(s[i])) % mod #文字ではなく数字のリストの場合はord不要
        v = 1
        for i in range(l):
            pw[i+1] = v = v * base % mod
    def get(self, l, r): #S[l:r)indexでいうl文字目からr-1文字目
        return (self.h[r] - self.h[l] * self.pw[r-l]) % self.mod

base1 = 1007; base2 = 2009
mod1 = 1000000007; mod2 = 1000000009

def main():
    N,M = map(int,input().split())
    S = []
    RHS = []
    for i in range(N):
        s = str(input())
        S.append(s)
        temp = RollingHash(s,base1,mod1)
        RHS.append(temp.get(0,M))

    
    ans = set([])
    mae = S[0]
    for i in range(26):
        na = chr(i+97) + mae
        #print(na)
        frh = RollingHash(na[:-1],base1,mod1)
        first = frh.get(0,M)
        srh = RollingHash(na[1:],base1,mod1)
        second = srh.get(0,M)
        for j in range(1,N):
            if RHS[j] == first or RHS[j] == second:
                continue
            else:
                break
        else:
            ans.add(na)
    
    ato = S[0]
    for i in range(26):
        na = ato + chr(i+97)
        #print(na)
        frh = RollingHash(na[:-1],base1,mod1)
        first = frh.get(0,M)
        srh = RollingHash(na[1:],base1,mod1)
        second = srh.get(0,M)
        for j in range(1,N):
            #print(RHS[j],first,second)
            if RHS[j] == first or RHS[j] == second:
                continue
            else:
                break
        else:
            ans.add(na)

    print(len(ans))


if __name__ == '__main__':
    main()